Field of Invention
The present invention relates to a proximity sensing device, especially a proximity sensor including a light guide unit which includes a partial-transmissive-partial-reflective (PTPR) optical element such that light emitted from a light source and light reflected from an object pass through the same window to reduce the area required for the window.
Description of Related Art
Proximity sensing devices are commonly employed in current handheld devices. On the housing of the handheld device, a conventional proximity sensing device requires two separate windows, one for emitting a light beam to outside of the device and the other for receiving light reflected from an outside object. In some design the two separate windows are shown to be one slot-shaped area on the outer appearance of the handheld device, but actually it includes two separate light passages. The total size of the two separate windows or the slot-shaped area is about 2.2-4 mm in its longer dimension. Apparently, this is disadvantageous in terms of minimizing the size providing flexibility in appearance design of a handheld device.